Rachael C. Shaw

The Evolution of Self-Control

Significance Although scientists have identified surprising cognitive flexibility in animals and potentially unique features of human psychology, we know less about the selective forces that favor cognitive evolution, or the proximate biological mechanisms underlying this process. We tested 36 species in two problem-solving tasks measuring self-control and evaluated the leading hypotheses regarding how and why cognition evolves. Across species, differences in absolute (not relative) brain volume best predicted performance on these tasks. Within primates, dietary breadth also predicted cognitive performance, whereas social group size did not. These results suggest that increases in absolute brain size provided the biological foundation for evolutionary increases in self-control, and implicate species differences in feeding ecology as a potential selective pressure favoring these skills. Cognition presents evolutionary research with one of its greatest challenges. Cognitive evolution has been explained at the proximate level by shifts in absolute and relative brain volume and at the ultimate level by differences in social and dietary complexity. However, no study has integrated the experimental and phylogenetic approach at the scale required to rigorously test these explanations. Instead, previous research has largely relied on various measures of brain size as proxies for cognitive abilities. We experimentally evaluated these major evolutionary explanations by quantitatively comparing the cognitive performance of 567 individuals representing 36 species on two problem-solving tasks measuring self-control. Phylogenetic analysis revealed that absolute brain volume best predicted performance across species and accounted for considerably more variance than brain volume controlling for body mass. This result corroborates recent advances in evolutionary neurobiology and illustrates the cognitive consequences of cortical reorganization through increases in brain volume. Within primates, dietary breadth but not social group size was a strong predictor of species differences in self-control. Our results implicate robust evolutionary relationships between dietary breadth, absolute brain volume, and self-control. These findings provide a significant first step toward quantifying the primate cognitive phenome and explaining the process of cognitive evolution.

Evidence suggesting that desire-state attribution may govern food sharing in Eurasian jays

State-attribution is the ability to ascribe to others an internal life like one’s own and to understand that internal, psychological states such as desire, hope, belief, and knowledge underlie others’ actions. Despite extensive research, comparative studies struggle to adequately integrate key factors of state-attribution that have been identified by evolutionary and developmental psychology as well as research on empathy. Here, we develop a behavioral paradigm to address these issues and investigate whether male Eurasian jays respond to the changing desire-state of their female partners when sharing food. We demonstrate that males feed their mates flexibly according to the female’s current food preference. Critically, we show that the males need to see what the female has previously eaten to know what food she will currently want. Consequently, the males’ sharing pattern was not simply a response to their mate’s behavior indicating her preference as to what he should share, nor was it a response to the males’ own desire-state. Our results raise the possibility that these birds may be capable of ascribing desire to their mates.

Eurasian jays, Garrulus glandarius, flexibly switch caching and pilfering tactics in response to social context

Corvids such as jays and ravens cache food for future consumption and can remember the location of caches that they have seen others make. Given the risk of caches being pilfered by observers, corvids limit opportunities for conspecifics to witness caching events. Faced with cache protection tactics, pilferers should also utilize tactics to maximize their success. Cacher–pilferer interactions and their underlying cognition have largely been investigated in semisocial ravens, Corvus corax, and western scrub-jays, Aphelocoma californica. However to understand the factors influencing the development of these abilities, data are required from species that differ in their socioecology from ravens and western scrub-jays. In the current study, we tested the caching and pilfering behaviour of territorial Eurasian jays in two social contexts. In one context, subjects competed with a dominant conspecific, while in the other the same individuals interacted with a subordinate competitor. When subordinate, birds initially suppressed caching, before caching more in less exposed locations. In contrast, when socially dominant, birds cached more and moved items multiple times. As subordinate pilferers, birds took longer to approach cache sites and approached when the cacher was at a distance, while when dominant, birds rapidly approached the conspecifics’ cache sites, frequently when the cacher was still in the process of caching. Individual jays therefore flexibly switched caching and pilfering tactics in response to the relative dominance of their competitor. We discuss the implications of our results for competing theories on the origin of behavioural flexibility and its underlying complex cognition in the corvid lineage.

Careful cachers and prying pilferers: Eurasian jays (Garrulus glandarius) limit auditory information available to competitors

Food-storing corvids use many cache-protection and pilfering strategies. We tested whether Eurasian jays (Garrulus glandarius) reduce the transfer of auditory information to a competitor when caching and pilfering. We gave jays a noisy and a quiet substrate to cache in. Compared with when alone, birds cached less in the noisy substrate when with a conspecific that could hear but could not see them caching. By contrast, jays did not change the amount cached in the noisy substrate when they were with a competitor that could see and hear them caching compared with when they were alone. Together, these results suggest that jays reduce auditory information during caching as a cache-protection strategy. By contrast, as pilferers, jays did not attempt to conceal their presence from a cacher and did not prefer a silent viewing perch over a noisy one when observing caching. However, birds vocalized less when watching caching compared with when they were alone, when they were watching a non-caching conspecific or when they were watching their own caches being pilfered. Pilfering jays may therefore attempt to suppress some types of auditory information. Our results raise the possibility that jays both understand and can attribute auditory perception to another individual.

Cognitive test batteries in animal cognition research: evaluating the past, present and future of comparative psychometrics

AbstractFor the past two decades, behavioural ecologists have documented consistent individual differences in behavioural traits within species and found evidence for animal “personality”. It is only relatively recently, however, that increasing numbers of researchers have begun to investigate individual differences in cognitive ability within species. It has been suggested that cognitive test batteries may provide an ideal tool for this growing research endeavour. In fact, cognitive test batteries have now been used to examine the causes, consequences and underlying structure of cognitive performance within and between many species. In this review, we document the existing attempts to develop cognitive test batteries for non-human animals and review the claims that these studies have made in terms of the structure and evolution of cognition. We argue that our current test battery methods could be improved on multiple fronts, from the design of tasks, to the domains targeted and the species tested. Refining and optimising test battery design will provide many benefits. In future, we envisage that well-designed cognitive test batteries may provide answers to a range of exciting questions, including giving us greater insight into the evolution and structure of cognition.

Pilfering Eurasian jays use visual and acoustic information to locate caches

Abstract Pilfering corvids use observational spatial memory to accurately locate caches that they have seen another individual make. Accordingly, many corvid cache-protection strategies limit the transfer of visual information to potential thieves. Eurasian jays (Garrulusglandarius) employ strategies that reduce the amount of visual and auditory information that is available to competitors. Here, we test whether or not the jays recall and use both visual and auditory information when pilfering other birds’ caches. When jays had no visual or acoustic information about cache locations, the proportion of available caches that they found did not differ from the proportion expected if jays were searching at random. By contrast, after observing and listening to a conspecific caching in gravel or sand, jays located a greater proportion of caches, searched more frequently in the correct substrate type and searched in fewer empty locations to find the first cache than expected. After only listening to caching in gravel and sand, jays also found a larger proportion of caches and searched in the substrate type where they had heard caching take place more frequently than expected. These experiments demonstrate that Eurasian jays possess observational spatial memory and indicate that pilfering jays may gain information about cache location merely by listening to caching. This is the first evidence that a corvid may use recalled acoustic information to locate and pilfer caches.

Linking nest predation with brood parasitism in captive zebra finches: a multi-pair study

Zebra finches (Taeniopygia guttata) are social, colonial nesting birds with moderate levels of intraspecific brood parasitism reported in both wild and captive populations. In a previous study, individually housed, captive zebra finch pairs responded to nest removal during the egg-laying period by parasitising simulated active conspecific nests. In the study reported here, we investigated the role of nest loss as a proximate trigger for parasitism in a more naturalistic setting: small groups consisting of three pairs per aviary. In three of ten experimental trials, females responded to nest removal during the egg-laying period by laying eggs in active neighbouring nests. This rate of parasitism was lower than that reported previously for individually housed pairs, and aggressive interactions between hosts and putative parasites were also observed. The results provide further support for the Hamilton–Orians hypothesis for the evolutionary origin of brood parasitism and highlight the influence of social context on the expression of brood parasitic behaviour. Together with qualitative descriptions of several previously unreported behaviours associated with nesting and brood parasitism in captive zebra finches, these experiments provide a functional context and methodology for future studies on zebra finches as a potential new model for the ecology and evolution of brood parasitism.

How does cognition shape social relationships

The requirements of living in social groups, and forming and maintaining social relationships are hypothesized to be one of the major drivers behind the evolution of cognitive abilities. Most empirical studies investigating the relationships between sociality and cognition compare cognitive performance between species living in systems that differ in social complexity. In this review, we ask whether and how individuals benefit from cognitive skills in their social interactions. Cognitive abilities, such as perception, attention, learning, memory, and inhibitory control, aid in forming and maintaining social relationships. We investigate whether there is evidence that individual variation in these abilities influences individual variation in social relationships. We then consider the evolutionary consequences of the interaction between sociality and cognitive ability to address whether bi-directional relationships exist between the two, such that cognition can both shape and be shaped by social interactions and the social environment. In doing so, we suggest that social network analysis is emerging as a powerful tool that can be used to test for directional causal relationships between sociality and cognition. Overall, our review highlights the importance of investigating individual variation in cognition to understand how it shapes the patterns of social relationships. This article is part of the theme issue ‘Causes and consequences of individual differences in cognitive abilities’.

Can you teach an old parrot new tricks? Cognitive development in wild kaka (Nestor meridionalis)

Despite recent efforts to characterize innovative individuals within a species, we still know very little about the ontogeny of innovation ability. A number of studies have found that innovation rates are correlated with personality traits, such as neophilia and exploration. Juvenile birds are frequently more neophilic and explorative, yet few studies have found evidence of age-related differences in innovative problem-solving success. Here, we show consistently higher innovation efficiency in juveniles of a wild, omnivorous parrot species across a variety of tasks and contexts. We tested 104 kaka (Nestor meridionalis), ranging in age from four months to 13 years. Twenty-four individuals participated in all three of our problem-solving tasks, two of which involved a familiar feeder and one an entirely novel apparatus. Juveniles were the most efficient problem-solvers in all three tasks. By contrast, the adults’ success was context dependent and limited to the novel apparatus, which did not require modification of a pre-learned behavioural response. This suggests greater behavioural flexibility in the juvenile birds, who also showed higher persistence and exploratory diversity than adults. These traits may enable young kaka to discover efficient foraging techniques, which are then maintained throughout adulthood.

Male New Zealand robins ( Petroica longipes ) cater to their mate’s desire when sharing food in the wild

In many species that have bi-parental care, food-sharing males provide vital nutritional resources to their mates during reproduction. However, it is currently unknown whether females can signal specific desires to their mates, or if males can cater to female desire in the wild. Here we investigate whether and how wild male North Island robins (Petroica longipes) respond to changes in their mates’ desires and nutritional need when sharing food. We demonstrate that wild female robins’ desire for particular foods changes over short time periods; when given the choice between two types of insect larvae, females prefer the type they have not recently eaten. In our experiments, wild male robins preferentially shared the larvae type that their mate was most likely to desire and also increased the quantity of food shared if she had begun incubating. Males catered to their mates’ desire when female behaviour was the only cue available to guide their choices. This is the first evidence that females may behaviourally communicate their specific food desires to their mates, enabling males to cater to fine-scale changes in their mates’ nutritional requirements in the wild. Such a simple behaviour-reading mechanism has the potential to be widespread among other food-sharing species.